No medicinal cannabis for rheumatology patients

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The reason for the medical interest in herbal cannabis is that the human body has an extensive cannabinoid system comprising molecules and receptors that have effects on many functions including pain modulation. Medical cannabis is commonly used to self-treat severe pain associated with arthritis and musculoskeletal pain. As of June 2013, estimates from the office of Information Commissioner of Canada list “severe arthritis” as the reason the 65% of Canadians who are allowed to possess marijuana for medicinal purposes.

“With the public outcry for herbal cannabis therapy, governments around the world are considering its legalization for medicinal use,” explains lead investigator Dr. Mary-Ann Fitzcharles, a rheumatologist and researcher at the Research Institute of the MUHC and who is also a professor of medicine at McGill University. “Physicians caring for patients who are self-medicating with marijuana need to understand the health implications of using this drug. Our review aims to provide healthcare professionals with that medical evidence related to medical marijuana use in patients with rheumatic conditions.”

The present review examines the dosing, administration, efficacy and risks of herbal cannabis in pain management for patients with rheumatic conditions. Concentrations of tetrahydrocannabinol (THC)—the substance found in Cannabis sativa that provides pain relief and alters brain function (psychoactive effect)—vary in the plant material by up to 33% and absorption rates between 2% and 56%, making the dosing of herbal cannabis unreliable. While cannabis may be ingested, most users prefer to inhale the compound for a quicker response. However, smoking a “joint” is not recommended by the medical community due to adverse effects on the respiratory system from hydrocarbons, tar and carbon monoxide.

Furthermore, there is no formal short-term or long-term study of the effectiveness of herbal cannabis in patients with rheumatic diseases. Studies that show good efficacy of cannabinoids for cancer and neuropathic pain may not be extended to rheumatic diseases because of the differing mechanism in the types of pain.

The review authors highlight that use of medical marijuana comes with inherent risks such as compromised cognitive and psychomotor function. Long-term use of cannabis may lead to mental illness, dependence, addiction and memory issues.

“At this time, we cannot recommend herbal cannabis for arthritis pain management given the lack of efficacy data, potential harm from the drug, and availability of other therapies for managing pain,” concludes Dr. Fitzcharles. “Physicians should discourage rheumatology patients from using medical marijuana as a therapy.”